In the manufacture of a semiconductor device, a semiconductor die is bonded to a substrate such as a copper heatsink or a metallized ceramic intermediary. Typically, a bonding material, such as a tin solder, is interposed the die and substrate to bond the two bodies. In production applications where die bonding machines are used, solder preforms, comprising prefabricated tablets of the solder material, are employed to enable automation of the entire process.
Several problems exist using solder preforms, particularly with small, fragile semiconductor devices such as facet-emitting lasers and LEDs. The smallest preforms are generally about 25 micrometers (.mu.m) thick and are typically bowed due to uneven cooling during their fabrication. Preforms of this thickness generally result in the presence of solder on the die facets after bonding. Heating the substrate and solder beyond the solder melting point is effective in thinning out the solder but creates other problems. For example, when a tin solder preform is wetted to the substrate metallized with gold preparatory to die bonding, gold-tin intermetallic compounds are formed which are known to adversely affect the physical, electrical and thermal properties of the subsequent bond to the die.
Therefore, an improved method of bonding a semiconductor die to a substrate has been sought.